The present invention relates to anisotropic colorants and ink-jet ink compositions that comprise the anisotropic colorants. These anisotropic colorants are highly stable and can be designed to provide enhanced chroma, gloss, gloss uniformity, smearfastness, print quality, drytime, and improved resistance to water when applied to a media. Moreover, inks formulated with these new colorants are useful in ink-jet printing, including thermal ink jet printing, piezoelectric ink jet printing, and continuous ink jet printing.
Most colorants used commercially are either discreet dyes or dispersed pigments. In the case of the latter, the pigment particle is typically either dispersed with polymers (through non-covalent interactions), or modified covalently with solubilizing moieties (forming xe2x80x9cself-dispersedxe2x80x9d pigments). In neither instance is the resulting spatial homogeneity (or inhomogeneity) of the discreet particle a consideration.
This necessarily dictates that no order or structuring of the colorants on the printed substrate can subsequently be imposed. This is an important point, because it places hard limits on certain performance attributes of the pigments, in particular chroma and gloss (and gloss uniformity). Pigments are well known in the industry to be inferior to dyes with respect to chroma and gloss on non-specialized media. Part of this lack of performance can be attributed directly to the amorphous nature of the pigment itself and the consequent amorphous nature of the pigment ensemble on the substrate.
Ink-jet printers offer a low cost, high quality, and comparatively noise-free option to other types of printers commonly used with computers. Such printers employ a resistor element in a chamber provided with an egress for ink to enter from a plenum. The plenum is connected to a reservoir for storing the ink. A plurality of such resistor elements are arranged in a particular pattern, called a primitive, in a printhead. Each resistor element is associated with a nozzle in a nozzle plate, through which ink is expelled toward a print medium. The entire assembly of printhead and reservoir comprise an ink-jet pen.
On operation, each resistor element is connected via a conductive trace to a microprocessor, where current-carrying signals cause one or more selected elements to heat up. The heating creates a bubble of ink in the chamber, which is expelled through the nozzle toward the print medium. In this way, firing of a plurality of such resistor elements in a particular order in a given primitive forms alphanumeric characters, performs area-fill, and provides other print capabilities on the medium.
Ink-jet inks used in thermal ink-jet printing typically comprise a colorant and a vehicle, with the vehicle often containing water and other relatively low surface tension liquids.
As noted above, there are two general classifications of colorants: dye-based and pigment-based. Dyes have the advantage of being water-soluble. However, problems with dyes include poor waterfastness, poor smearfastness, poor bleed control between colors, and poor lightfastness. Pigments are generally water-insoluble and require a dispersant or other means to make it soluble in water. For the non-covalently dispersed pigments, the nature of the dispersant and the mass ratio of pigment to dispersant are the factors that are controlled. For the self-dispersed pigments, the nature of the covalently-attached solubilizing groups and their density on the pigment surface are the factors that are controlled. From the colorant""s frame of reference, these modifications are spatially random by their nature. The resulting pigments are thus a statistical ensemble of the dispersion processes.
Although the relevant art contains many examples of ink-jet ink formulations using these colorants, a need exists for ink compositions comprising stable, water soluble colorants which provide improved chroma, gloss, gloss uniformity, smearfastness, print quality, drytime, and improved resistance to water when applied to a media.
In accordance with the invention, an ink-jet ink composition is provided which comprises a colorant that is both water-soluble and contains discreet, specifically attached substituents on the colorant particle. These attachments may be homogeneously or inhomogeneously arranged on the particle; however the attachments are not randomly attached like typical pigments used heretofore.
In this embodiment, colorants are synthesized, dispersed, or modified in such a fashion that the resulting discreet particles are anisotropic with respect to their dispersants, polymers, or other attached additives. In other words, on a microscopic or molecular level, one or more xe2x80x9csidesxe2x80x9d or xe2x80x9cfacesxe2x80x9d of the particle are purposefully chemically/physically distinct from another face or faces. Restating this, the dispersion process is now meant to impart anisotropy, distinct morphology, and/or chirality to the pigment. This is done with the purpose to impart 2- and 3-dimensional structure to the resulting printed substrate.
By creating anisotropic colorants, and thereby influencing the resulting orientation of the particles on the substrate, it is possible to change the surface energy of the printed substrate to a substantial degree. This results in improvements to properties such as improved waterfastness, smearfastness, chroma, and gloss.
One can design specific sites or faces on the colorant to interact preferentially with the substrate, the environment, or both. Surfactant-like molecules may be attached to one side of the colorants to xe2x80x9canchorxe2x80x9d it to the substrate, while hydrophobic or non-wetting moieties (fluoropolymers, siloxanes, etc.) can be designed to be present on the surface.
There are several ways that the colorants of this invention may be dispersed anisotropically. While these methods are known in art of molecule design and synthesis, examples include:
the presence of steric bulk on a dispersant, such that the region around the attachment site is no longer available for subsequent reactions. This may also be envisioned as a partial encapsulation.
the use of biphasic or heterogeneous reactions, in which only part of the pigment surface is exposed toward the reactants.
modification of the entire surface of a larger particle with subsequent break up, thereby exposing unreacted surfaces.
Inks comprising these anisotropic colorants are very effective in reducing smear and have increased waterfastness, gloss, gloss uniformity, and improved print quality. The ink may contain further components to aid in providing improved print quality and performance in an ink-jet printer.
Additionally, a method of ink-jet printing which uses the disclosed inks and exploits the inks"" properties is provided.
All concentrations herein are in weight percent, unless otherwise indicated. The purity of all components is that employed in normal commercial practice for ink-jet inks. All references are hereby incorporated by reference.
One example of anisotropic colorants useful herein include modified black pigments obtained from colorant vendors such as Cabot Corp. and Orient Chemical. Many pigments are useful in the practice of this invention. The following pigments comprise a partial list of useful colorants in this invention.
Paliogen(copyright) Orange, Heliogen(copyright) Blue L 6901F, Heliogen(copyright) Blue NBD 7010, Heliogen(copyright) Blue K 7090, Heliogen(copyright) Blue L 7101F, Paliogen(copyright) Blue L 6470, Heliogen(copyright) Green K 8683, and Heliogen(copyright) Green L 9140, are all available from BASF Corp.
The following pigments are available from Cabot: Monarch(copyright) 1400, Monarch(copyright) 1300, Monarch(copyright) 1100, Monarch(copyright) 1000, Monarch(copyright) 900, Monarch(copyright) 880, Monarch(copyright) 800, and Monarch(copyright) 700.
The following pigments are available from Ciba: Chromophtal(copyright) Yellow 3G, Chromophtal(copyright) Yellow GR, Chromophtal(copyright) Yellow 8G, Igrazin(copyright)D Yellow 5GT, Igralite(copyright) Rubine 4BL, Monastral(copyright) Magenta, Monastral(copyright) Scarlet, Monastral(copyright) Violet R, Monastral(copyright) Red B, and Monastral(copyright) Violet Maroon B.
The following pigments are available from Columbian: Raven 7000, Raven 5750, Raven 5250, Raven 5000, and Raven 3500. The following pigments are available from Degussa: Color Black FW 200, Color Black FW 2, Color Black FW 2V, Color Black FW 1, Color Black FW 18, Color Black S160, Color Black FW S170, Special Black 6, Special Black 5, Special Black 4A, Special Black 4, Printex U, Printex 140U, Printex V, and Printex 140V. Tipure(copyright) R-101 is available from Dupont. The following pigments are available from Heubach: Dalamar(copyright) Yellow YT-858-D and Heucophthal(copyright) Blue G XBT 583D. The following pigments are available from Hoechst: Permanent Yellow GR, Permanent Yellow G, Permanent Yellow NCG-71, Permanent Yellow GG, Hansa Yellow RA, Hansa Brillant Yellow 5GX-02, Hansa Yellow-X, Novoperm(copyright) Yellow HR, Novoperm(copyright) Yellow FGL, Hansa Brilliant Yellow 10GX, Permanent Yellow G3R-01, Hostaperm(copyright) Yellow H4G, Hostaperm(copyright) Yellow H3G, Hostaperm(copyright) Orange GR, Hostaperm(copyright) Scarlet GO, and Permanent Rubine F6B. The following pigments are available from Mobay: Quindo(copyright) Magenta, Indofast(copyright) Brilliant Scarlet, Quindo(copyright) Red R6700, Quindo(copyright) Red R6713, Indofast(copyright) Violet. The following pigments are available from Sun Chemical: L74-1357 Yellow, L75-1331 Yellow, and L75-2577 Yellow.
For instance, the anisotropic colorants for use in the present ink formula may comprise chemical modifications to impart water solubility to the particle. Under typical chemical processes, the resulting surface of the pigment consists of randomly placed hydrophilic substituents, such as carboxylate, phosphate, and/or sulfonate functionalities for anionic pigments, and ammonium, quaternary ammonium, or phosphonium functionalities for cationic pigments. For this invention the water solubility substituents would be covalently attached on the pigment particle in discreet locations on the surface, while a hydrophobic substituent could be placed in specially selected sites adjacent to or opposing the hydrophilic sites. Thus allowing the pigment to be water soluble and suitable for ink-jet ink formulations, yet when applied to the media to spatially arrange itself such that the hydrophobic side provided waterfastness to the printed ink.
See U.S. Pat. Nos. 5,707,432; 5,630,868; 5,571,311; and 5,554,739 for a discussion of modified carbon black pigments and methods of attaching the functionalized groups.
To be useful in ink formulations to be ink-jettable, the colorant particles of the present invention preferably have a useful mean diameter ranging from about 0.005 to about 12 um. Colorants of this type result from chemical reactions where solvent-accessible functional groups are derivatized to provide solubilizing groups that render the colorant soluble in water.
Ink-jet Ink Vehiclexe2x80x94The ink compositions of this invention comprise the anisotropic colorants above plus a vehicle. For a discussion of inks and their properties, see The Printing Manual, 5th ed. Leach et al. (Chapman and Hall, 1993). See also U.S. Pat. Nos. 2,833,736; 3,607,813; 4,104,061; 4,770,706; and 5,026,755. Examples of components in the ink vehicle include surfactants, co-solvents, buffers, biocides, colloids, viscosity modifiers, and mixtures thereof.
The inks of the present invention typically comprise about 1 to about 20 wt % water-miscible organic co-solvent. More preferably, the inks comprise about 3 to 15 wt % organic co-solvent.
The water-miscible organic co-solvents suitably employed in the practice of the present invention include any of, or a mixture of two or more of, such compounds as nitrogen-containing ketones, such as 2-pyrrolidone, N-methyl-pyrrolid-2-one (NMP), 1,3-dimethylimidazolid-2-one, and octyl-pyrrolidone; diols such as ethanediols (e.g., 1,2-ethanediol), propanediols (e.g., 1,2-propanediol, 1,3-propanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol, ethylhydroxy-propanediol (EHPD)), butanediols (e.g., 1,2-butanediol, 1,3-butanediol, 1,4-butanediol), pentanediols (e.g., 1,2-pentanediol, 1,5-pentanediol), hexanediols (e.g., 1,2-hexanediol, 1,6-hexanediol, 2,5-hexanediol), heptanediols (e.g., 1,2-heptanediol, 1,7-heptanediol), octanediols (e.g., 1,2-octanediol, 1,8-octanediol); alcohols, such as C3-C6 alcohols (e.g., propanol, butanol, pentanol, and hexanol), including isomers thereof (e.g., 1-propanol and 2-propanol); glycol ethers and thioglycol ethers commonly employed in ink-jet inks, such as polyalkylene glycols such as polyethylene glycols (e.g., diethylene glycol (DEG), triethylene glycol, tetraethylene glycol), propylene glycols (e.g., dipropylene glycol, tripropylene glycol, tetrapropylene glycol), polymeric glycols (e.g., PEG 200, PEG 300, PEG 400, PPG 400), and thiodiglycol. Additional co-solvents include hydantoins (glycol ureas) and derivatives thereof, such as a hydantoin containing ethyl hydroxide and methyl groups, available from Lonza, Inc. as Dantocol DHE, and polyalkoxylated triols, such as Multranol 4012, which is a polyalkoxylated triol having a molecular weight of about 440, available from Bayer.
Other classes of cosolvents employed in the practice of this invention include, but are not limited to, caprolactams, formamides, acetamides, and long chain alcohols.
Preferably, the organic co-solvent comprises a mixture of 2-pyrrolidone and 1,6-hexanediol.
Buffers optionally employed in the practice of this invention to modulate pH can be organic-based biological buffers or inorganic buffer, preferably organic-based. Examples of buffers include tris(hydroxymethyl)aminomethane, available from companies such as Aldrich Chemical (Milwaukee, Wis.), 4-morpholineethanesulfonic acid (MES), and 4-morpholinepropanesulfonic acid (MOPS).
Metal chelators optionally employed in the practice of this invention are used to bind transition metal cations that may be present in the ink. Examples of preferably-employed metal chelators include: EDTA, Diethylenetetraaminepentaacetic acid (DTPA), trans-1,2-diaminocyclohexanetetraacetic acid (CDTA), (ethylenedioxy) diethylene dinitrilotetraacetic acid (EGTA), malonic acid, salicylic acid, or other chelators that can bind transition metal cations.
Any of the biocides commonly employed in inkjet ink may optionally be employed in the practice of this invention, such as Nuosept 95, available from Huls America (Piscataway, N.J.); Proxel GXL, available from Zeneca (Wilmington Del.); and glutaraldehyde, available from Union Carbide Company (Bound Brook, N.J.) under the trade designation Ucarcide 250.
The color inks of the present invention may further comprise one or more surfactants, the total surfactant concentration ranging from about 0.05 to 6 wt %. The surfactant mixture may comprises anionic, non-ionic, amphoteric, and fluoro-surfactants. U.S. Pat. No. 5,106,416, discloses more fully most of the surfactants listed above.
One example of a suitable non-ionic surfactant includes the SURFYNOL series, which are acetylenic ethoxylated diols available from Air Products. Another example of a suitable non-ionic surfactant includes the TERGITOL series, which are polyethylene or polypropylene oxide ethers available from Union Carbide.
One example of a suitable anionic surfactant includes the DOWFAX series, which are diphenyl sulfonate derivatives available from Dow Chemical. Another example of a suitable anionic surfactant is the OT series, which are dioctyl sodium sulfosuccinates available from Cytec Ind.
Preferred fluoro-surfactants include ZONYL FSA, ZONYL FS-62, and FLUORAD FC-129.
A typical formulation for an ink useful in the practice of the invention includes the colorant (about 0.001% to 10 wt %), one or more cosolvents, one or more water-soluble surfactants/amphiphiles, optionally one or more high molecular weight colloids (0 to about 3 wt %), and water (balance).
Between 0 and about 3 wt % of a high molecular weight colloid derived from natural or synthetic sources may optionally be added to the ink formulation. Addition of a high molecular weight colloid improves print quality. Example of high molecular weight colloids employed in the practice of this invention include alginates, mannuronic acid, carageenan, guar gum, xanthan gum, dextran, chitin, chitosan, carboxymethylcellulose, nitromethylcellulose, and all derivatives thereof. These colloids are disclosed in U.S. Pat. No. 5,133,803, xe2x80x9cHigh Molecular Weight Colloids for Bleed Control.xe2x80x9d The preferred concentration of the high molecular weight component colloid in the inks of this invention is from 0% to about 0.75 wt %.
Other known additives such as viscosity modifiers and other acrylic or non-acrylic polymers may be added to improve various properties of the ink compositions as desired.
The inks are formulated by combining the various components of the vehicle and mixing them with the colorants disclosed herein. Ink formulations which employee the colorants generally have a pH from about 3 to about 12. The viscosity of the final ink composition is from about 0.8 to about 8 cps, preferably from about 0.9 to about 4 cps.
A method of ink-jet printing is also disclosed herein. The inks of this invention may be used in any conventional ink-jet or bubble-jet or piezoelectric printer. Preferably the inks are used in thermal ink-jet printers. The ink is typically charged into a printer cartridge and printed on any medium. Examples of suitable media for printing includes paper, textiles, wood, and plastic.